NEW YORK -- Former Oakland Athletics sluggers Jose Canseco, Mark McGwire and Jason Giambi were among seven current and former baseball stars that a congressional committee plans to subpoena as soon as Wednesday to testify about steroids.

Curt Schilling, Sammy Sosa, Rafael Palmeiro and Frank Thomas also were asked last week to testify. Thus far, only Canseco and Thomas have said they were willing to appear.

"We hope subpoenas won't be necessary, but we are prepared to move forward with subpoenas [Wednesday] if we receive information that witnesses are not willing to appear voluntarily," David Marin, a spokesman for House Government Reform Committee chairman Rep. Tom Davis, said Tuesday.

The Baltimore Sun first reported on the subpoenas earlier Tuesday on its Web site.

According to reports, Barry Bonds, whose role in baseball's steroids scandal has been questioned for the last year, has not yet been subpoenaed.

Lawyers for the baseball commissioner's office and players' association attempted to negotiate a joint response to the committee, which last week invited the players and several officials to appear at the March 17 hearing.

Baseball commissioner Bud Selig, union head Donald Fehr, baseball executive vice president Sandy Alderson and San Diego general manager Kevin Towers also were asked to testify.

Giambi testified before a federal grand jury investigating steroids in 2003 and, according to a report by the San Francisco Chronicle in December, told the panel he had used steroids. Giambi has not denied the report but has refused to publicly discuss steroids, citing advice from his lawyers.

Giambi was granted limited immunity by prosecutors for his grand jury testimony. Because of the ongoing investigation, it is possible the Justice Department, the committee and Giambi might have to negotiate an immunity agreement before he would answer questions from the congressional panel.

If he is granted immunity and testifies publicly, the Yankees potentially could use any admissions as grounds to attempt to void his contract, which has four years and $82 million remaining.

In his book released last month, "Juiced: Wild Times, Rampant 'Roids, Smash Hits & How Baseball Got Big," Canseco admits using steroids and alleges that McGwire often injected the drugs with him. Canseco also said he introduced steroids to former Texas Rangers teammates, including Palmeiro.

Palmeiro, McGwire, Ivan Rodriguez, Bret Boone and others named by Canseco have denied using the performance-enhancing drugs.

Also Tuesday, the parents of two amateur players who committed suicide were added as witnesses.

Taylor Hooton, a cousin of former major leaguer Burt Hooton, was 17 when he hanged himself on July 15, 2003, and his parents think the suicide was due to depression that followed Taylor's end of steroid use. Rob Garibaldi, who played for the University of Southern California, was 24 when he shot himself on Oct. 1, 2002, and his parents also think his death was related to steroids.

"I believe it is important for the committee to hear from medical experts and impacted families on the scope of the steroid problem nationwide," Davis said.

Three medical experts also were added: Dr. Gary Wadler of the World Anti-Doping Agency, Dr. Nora Volkow of the National Institutes of Health and Dr. Kirk Brower of the University of Michigan Medical School.

"These witnesses have voluntarily agreed to share their expertise and experiences with the Committee, and I hope the players and league officials will follow suit," said Rep. Henry Waxman, the ranking Democrat on the committee.